1. Field of the Invention
The present invention relates to a test head of an IC test device, particularly to that for carrying out a high speed functional test of a device under test (hereinafter referred to as DUT) such as a memory and also a DC test.
2. Prior Art
An IC test device comprises generally, as shown in FIG. 3, a CPU 1, a pattern generator 2, a decision device 3, a driver.comparator circuit 4 composed of a driver 4A and a comparator 4B, a power supply 14, a terminating resistor 5, a terminating resistor intermittent relay 6, a DC measuring circuit intermittent relay 7, a DC measuring circuit 8 for carrying out a high speed functional test and a DC test of a DUT 9.
The CPU 1 is connected to the driver 4A of the driver.comparator circuit 4 by way of the pattern generator 2, and it is also connected to the comparator 4B of the driver.comparator circuit 4 by way of the decision device 3.
The DUT 9 is connected to the terminating resistor 5 by way of the terminating resistor intermittent relay 6, and the terminating resistor 5 is connected to the power supply 14.
The DUT 9 is also connected to the DC measuring, circuit 8 by way of the DC measuring circuit intermittent relay 7, and the DC measuring circuit 8 is connected to the CPU 1. The IC test device having such a construction carries out the high speed functional test and the DC test of the DUT 9 in accordance with a test program which is inputted to the CPU 1.
First of all, when the high speed functional test is carried out, in FIG. 3, the terminating resistor intermittent relay 6 is turned on to terminate at the terminating resistor 5 having a resistance value RE which is substantially the same as characteristic impedance ZO of a signal line extending from the driver.comparator circuit 4 to the DUT 9, so that an impedance matching between the characteristic impedance ZO and the resistance value RE is performed while the DC measuring circuit intermittent relay 7 is turned off to be disconnected from the DC measuring circuit 8.
In this state, measuring frequency information which is set by the CPU 1 is supplied to the pattern generator 2, while the information concerning a driver level and a comparator level is supplied from the CPU 1 to the driver.comparator circuit 4, wherein a test pattern signal of the measuring frequency information is generated in the pattern generator 2. The test pattern signal is amplified to the extent of a driver level which is set by the driver 4A of the driver.comparator circuit 4, and the same signal is inputted to the DUT 9.
As a result, an output pattern signal from the DUT 9 is inputted to the comparator 4B of the driver.comparator circuit 4, and it is compared with a set comparator level, and the result of comparison is stored in the decision device 3, so that a yes-no decision of the high speed functional test of the DUT 9 is notified to the CPU 1.
In case that the DC test is carried out next, the terminating resistor intermittent relay 6 is turned off to disconnect the DUT 9 from the terminating resistor 5, thereby eliminating the influence by the terminating resistor 5 while the DC measuring circuit intermittent relay 7 is turned on to connect the DUT 9 to the DC measuring circuit 8.
When a voltage or a current is supplied to the DUT 9, the DC test is carried out by the DC measuring circuit 8, and the result, of the test is notified to the CPU 1.
In such an IC test device, the conventional test head has constructions set forth in FIG. 2(A) and FIG. 2(B).
That is, a pin card 12 is secured to the DUT board 11, and an IC circuit 10 and driver.comparator circuit 4 are respectively mounted on an inner side 12A of the pin card 12.
When the driver.comparator circuit 4 and the IC circuit 10 are connected to each other by a conductive pattern (not shown) provided on the inner side 12A of the pin card 12, the driver.comparator circuit 4 is connected to the DUT 9 by way of the IC circuit 10.
Meanwhile, the terminating resistor intermittent relay 6, the terminating resistor 5 and the DC measuring circuit intermittent relay 7 are respectively mounted on an outer side 12B of the pin card 12, and these elements are respectively connected to the IC circuit 10 mounted on the inner side 12A by a conductive pattern (not shown) provided on the outer side 12B and a through hole 13 (see FIG. 2(B)).
In other words, a measuring line extending from the driver.comparator circuit 4 mounted on the inner side 12A to the terminating resistor 5 mounted on the outer side 12B by way of the DUT 9 mounted on the IC circuit 10 is relayed by the through hole 13.
The pin card 12 which mounts the driver.comparator circuit 4, etc. on the inner side 12A and outer side 12B thereof is fixed to the DUT board 11 by way of an opening 40 in plural numbers, wherein the high speed functional test and the DC test are respectively carried out for a plurality of DUTs 9.
The driver.comparator circuit 4, etc. constituting the conventional test head are respectively mounted on both surfaces of the pin card 12, thereby reducing the distance between the driver.comparator circuit 4, etc. and the DUT 9.
That is, when the elements such as the driver.comparator circuit 4, etc. are mounted on the inner side 12A alone or the outer side 12B alone of the pin card 12, the distance between the driver.comparator circuit 4, etc. and the DUT 9 is liable to increase. Further, if the elements are mounted on one surface alone of the pin card 12, the mounting space is restricted so that all the elements from the driver.comparator circuit 4 to the terminating resistor 5 (see FIG. 2(A) and FIG. 2(B)) cannot be mounted on the pin card 12.
Because of the mounting of the elements on both surfaces of the pin card 12, the measuring line extending from the driver.comparator circuit 4 mounted on the inner side 12A of the pin card 12 to the terminating resistor 5 mounted on the outer side 12B of the pin card 12 by way of the DUT 9 is not connected by the conductive pattern alone but connected by way of the through hole 13 (see FIG. 2(C)).
As a result, since there occurs an impedance mismatching between the characteristic impedance ZO and the resistance value RE, when the terminating resistor intermittent relay 6 is turned on while the DC measuring circuit intermittent relay 7 is turned off (see FIG. 2(C)) so as to carry out a high speed functional test of the DUT 9, if the high frequency test pattern signal outputted from the driver 4A constituting the driver.comparator circuit 4 is inputted to the DUT 9, the high frequency test pattern signal is reflected, thereby deteriorating measuring accuracy.